LASER EXTRACTOR FOR AN IMPLANTED OBJECT

Abstract: A lead extraction device which utilizes laser (8) energy to separate an implanted object, such as a pacemaker lead (2), from fibrous scar tissue and thereby permit the implanted object to be extracted from a body. The extraction device features a catheter (1) having a central lumen (31). The lumen is preferably dimensioned so a pacemaker lead will fit within. The catheter is thereby guided by the lead. The catheter has at least one optical fiber (23) to emit laser energy from the distal end and thereby separate the lead from fibrous scar tissue. Disclosed embodiments include catheters which emit light parallel as well as inwardly perpendicular to the catheter and the lead. Through such catheters the lead may be separated along its length, as well as separated at its distal end from fibrous scar tissue, thereby permitting the lead to be readily extracted from the body.

Description: LASER EXTRACTOR FOR AN IMPLANTED OBJECT REFERENCE TO RELATED APPLICATIONS This is a continuation-in-part of co-pending application serial number 08/131,055 entitled "LASER EXTRACTOR FOR AN IMPLANTED OBJECT" of Wahlstrom et al. filed October 1, 1993 and is related to application serial number 08/153,715 entitled "HEART SYNCHRONIZED EXTRACTOR FOR AN IMPLANTED OBJECT" of Wahlstrom et al. filed November 16, 1993. BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a method and apparatus for removal of an implanted object from a patient's body and specifically for removal of transvenous endocardial leads from a patient's heart and the venous paths thereto. Generally speaking, a lead permits an implantable pulse generator, commonly known as a pacemaker, to stimulate the heart. More specifically an endocardial lead provides an electrical pathway between the pacemaker, connected to the proximal end of the lead, and endocardial tissue, in contact with the distal end of the lead. Endocardial tissue refers to a specific layer of tissue in the interior of the heart's chambers. In such a manner electrical pulses emitted by the pacemaker travel through the endocardial lead and stimulate the heart. Endocardial leads are often placed in contact with the endocardial tissue by passage through a venous access, such as the subclavian vein or one of its tributaries. Thus a transvenous endocardial lead refers to a pacemaker lead which contacts endocardial tissue through a vein. In the past, various types of transvenous endocardial leads have been introduced into different chambers of the heart including the right ventricle, right atrial appendage and atrium as well as the coronary sinus. These leads usually are composed of an insulator sleeve that contains a coiled conductor having an electrode tip attached at the distal end. The electrode tip is held in place within the trabeculations of endocardial tissue. The distal ends of many available leads include flexible tines, wedges, or finger-like projections which extend radially outward and usually are molded from and integral with the insulator sleeve of the lead. These tines allow better containment by the trabeculations of endocardial tissue and help prevent dislodgement of the lead tip. Once an endocardial lead is implanted within a chamber, the body's reaction to its presence furthers its fixation within the heart. Specifically, shortly after placement, i.e. acute placement, a blood clot forms about the flanges or tines due to enzymes released in response to the irritation of the endocardial tissue caused by electrode tip. Over time, i.e. during chronic implantation, fibrous scar tissue eventually forms over the distal end, usually in three to six months. In addition, fibrous scar tissue often forms, in part, over the insulator sleeve within the venous system and the heart chamber. Such tissue fixes the electrode tip within the heart during the life of the lead. Although the state of the art in implantable pulse generator or pacemaker technology and endocardial lead technology has advanced considerably, endocardial leads nevertheless occasionally fail, due to a variety of reasons, including insulation breaks, breakage of the inner helical coil conductor thereof and an increase in electrode resistance. Also, in some instances, it may be desirable to electronically stimulate different portions of the heart than that being stimulated with leads already in place. Due to these and other factors, therefore, a considerable number of patients may come to eventually have more than one, and sometimes as many as four or five, unused leads in their venous system and heart. Unused transvenous leads increase the risk complications will develop. Possible complications associated with leaving unused leads in the heart and venous system include an increased likelihood an old lead may be the site of infection. Development of an infection may, in turn, lead to septicemia, a possibly fatal complication. Unused leads may also cause endocarditis. Furthermore, unused leads may entangle over time, thereby increasing the likelihood of blood clot formation. Such clots may embolize to the lung and produce severe complications or even fatality. The presence of unused leads in the venous pathway and inside the heart can also cause considerable difficulty in the positioning and attachment of new endocardial leads in the heart. Moreover, multiple leads within a vein or artery may impede blood flow causing fatigue, weakness or dizziness within the patient. Further description and detail concerning the complications associated with unused leads left in place may be found in "Lead Extraction", Byrd et al.. Cardiology Clinics, Vol. 10, No. 4, Nov., 1992, incorporated herein by reference. As serious as the risks associated with leaving an unused lead in place may be, the risks associated with past methods and devices for lead removal were often greater. One technique used to remove a lead was to apply traction and rotation to the outer free end of the lead. This technique, however, could only be done before the lead tip became fixed in the trabeculations of endocardial tissue by large clot development. Clot development, however, is difficult to detect. Even shortly after lead implantation there exists the risk a clot has formed. Removal of a lead at that time may cause various sized emboli to pass to the lungs, possibly producing severe complications. In cases where the lead tip has become attached by fibrous scar tissue to the heart wall, removal of the lead has presented further major problems and risks. Porous lead tips may have an ingrowth of fibrous scar tissue attaching them to the heart wall. Sufficient traction on such leads in a removal attempt could cause disruption of the wall prior to release of the affixed lead tip, causing fatality. Even if the tines of the leads are not tightly scarred to the heart wall similar risks are faced. Moreover, lead removal may further be prevented by a channel of fibrotic scar tissue and endothelium surrounding the outer surface of the lead body and specifically the insulator sleeve, as mentioned above, at least partway along the venous pathway. Such "channel scar" tissue prevents withdrawal because of encasement of the lead. Continual strong pulling or twisting of the proximal free end of the lead could cause rupturing of the right atrial wall or right ventricular wall. Encasement by fibrous scar tissue in the venous pathway and in the trabeculations of cardiac tissue typically occurs within three to six months after the initial placement of the lead. The great risks presented by lead removal using traction and rotation techniques are such that if it becomes imperative to remove a lead (as in the case of septicemia) those doctors who have not focused and developed a specialty in lead removal often elect to have the patient's chest opened and the lead surgically removed rather than attempt removal using traction and rotation techniques. Even those doctors who have developed a specialty in lead removal sometimes elect to have the lead surgically removed rather than face the many risks presented. Description of the Prior Art As discussed above, many of the prior methods and devices for lead removal involved the application of traction or rotation or both to the lead. U.S. Patent No. 4,574,800 to Peers-Trevarton, incorporated herein by reference, discloses a lead extraction device constructed to fit within the central lumen of a lead conductor coil and wedge a distal portion of such device in the distal portion of the lead. Such an arrangement permits traction force to be transmitted from the proximal end of the device to the distal portion of the lead. This avoids the need to impart any substantial pulling forces along the length of the lead. As mentioned above, pulling along the lead body may result in rupture of the lead, possibly resulting in the conductor coil to unwind within a patient. Further patents have disclosed variations on the concept of engaging the distal portion of the lead, these include: U.S. Patent Nos. 5,207,683; 5,013,310; 4,988,347 and 4,943,289 to Goode et al. , each of which is incorporated herein by reference. The International Patent Application WO 91/19532 of Rackette, incorporated herein by reference, discloses a lead extraction device constructed to fit within the central lumen of a lead conductor coil and wedge a distal portion of such device in the distal portion of the lead. Such an arrangement permits a force to be transmitted from the proximal end of the lead extraction device to the distal portion of the lead. In addition, other devices have featured cutting surfaces to cut through the channel scar encasing the lead body and enveloping the tine assembly. For example, U.S. Patent Nos. 4,582,056; 4,576,162; and 4,471,777 to McCorkle, each of which is incorporated herein by reference, generally relate to lead extraction devices utilizing nesting catheters to grasp the lead and cut through, using an annular surface, such fibrous scar tissue and channel scar. U.S. Patent No. 5,011,482 to Goode et al., incorporated herein by reference, discloses a device having a series of tubes to separate the lead from fibrotic tissue, the second tube featuring a wire at the distal end to wipe across the face of the electrode and separate it therefrom. Such devices are heavily reliant, however, upon the skill and judgement of the operator in order to consistently and reliably separate the distal tip of the lead from fibrotic scar tissue without causing injury to the patient. Devices and techniques which rely upon traction, moreover, face a myriad of serious complications. Sustained traction to the lead, especially a lead secured by fibrous tissue at its distal end, may cause hypotension, chest pain or avulsion. Moreover if the ventricular wall is distorted, by traction to the lead, to proximate the tricuspid valve, low cardiac output may result. Failure of the lead, and thus the heart wall, to return to its original position may cause a hemodynamic emergency. Other complications include possible myocardial rupture and tamponade as well as lead breakage. Lead breakage is potentially very serious as rupture of the outer insulative sleeve may expose and allow conductor coil wire to uncoil. Exposed and uncoiled conductor coil wire presents a sharp and potentially very damaging surface to the cardiac and venous tissue. In such a situation full thoracic surgery is immediately required to remove the ruptured lead. Traction may also cause the distal portion of the lead to separate from the lead body without exposing uncoiled conductor coil. Such a free floating distal portion, however, bouncing within the ventricle, may cause ventricular arrythmia, may perforate the heart and may cause vegetation to develop, itself causing emboli to be transported to the lungs. It has been found laser light may be used to remove obstructions from within the venous system. U.S. Patent No. 5,188,632 to Goldenberg, incorporated herein by reference, discloses a fiber optic wave guide configured to fit within at least one lumen of a catheter for performing an angioplasty. U.S. Patent No. 5,188,634 to Hussein et al., incorporated herein by reference, discloses a catheter for ablating obstructing materials within a corporeal lumen, the catheter having an optical fiber to transmit laser energy to the site of the obstructive material. U.S. Patent No. 5,040,548 to Yock, incorporated herein by reference, discloses a catheter having an optical fiber to transmit laser energy to the site of a venous obstruction. This device, however, requires a guide wire to be first inserted into the patient's venous system. U.S. Patent No. 5,032,123 to Katz et al. discloses a laser catheter having a radially divergent treatment beam. In particular the catheter has a metal collar and quartz end cap. Metal collar is spaced back from the distal end of the catheter and stabilizes the optical fibers; quartz end cap is positioned at the distal most end of the catheter and is fitted over the ends of the optical fibers to diffuse the exiting laser light and provide the radially divergent treatment beam. U.S. Patent No. 5,263,953 to Grace et al. discloses a two-piece tip for a catheter which is used to illuminate and ablate intravascular regions. The tip features an inner band and an outer band. The inner band has a radial thickness several times the radial thickness of each optical fiber. The tip is designed to be introduced over a guide wire, so that there is no need for the laser energy to ablate tissues in the region immediately adjacent the tip of the catheter, including in the region immediately adjacent the distal end of the inner band without also ablating into the center lumen of the catheter. Further patents disclosing devices utilizing laser light to remove obstructions from the blood stream include U.S. Patent No. 5,203,779 to Muller; U.S. Patent No. 5,176,674 to Hofman; U.S. Patent No. 5,041,108 to Fox et al.; U.S. Patent No. 4,993,412 to Murphy-Chutorian; U.S. Patent No. 5,032,123 to Katz et al.; and U.S. Patent No. 4,834,093 to Littleford, dec. et al., each of which is incorporated herein by reference. The U.S. Patent No. 5,125,924 to Rudko, also incorporated herein by reference, discloses a heart-synchronized vacuum-assisted pulsed laser technique for transmyocardial revascularization. Due to the many complications these lead removal techniques and devices face, and the efficacy of using laser light to remove obstructions from within the venous system, devices and techniques have been developed to accomplish lead removal using laser light. For example, Rao in "Use of a Laser to Extract Unwanted Pacemaker Leads", Tex. Heart Inst. J. , Vol. 16, No. 3, 1989, incorporated herein by reference, discloses use of a laser introduced into the lumen of a coiled conductor of a lead to sever the distal portion of a lead and thereby permit removal of the lead body. The patent publication of Liebetruth et al., DD 281 500 A7, incorporated herein by reference, discloses a device similar to disclosed in the Rao publication in that it uses laser light to sever the distal portion of the lead from the lead body. Specifically a sleeve type guide cylinder having a axially movable piston to clamp along a portion of the lead is disclosed. An optical fiber which opens onto the lead where it is clamped is used to sever the lead at a position proximate the distal end. These devices, however, are specifically designed to sever the lead so that the distal portion may be abandoned within the heart. As discussed previously, permitting a severed lead tip to remain within the body, and especially within the right ventricle may lead to serious complications such as ventricular arrythmia, heart perforation and the development of emboli. Moreover, as disclosed in the article of Storm et al. entitled "A Severed Pacemaker Lead Entrapped in a Hepatic Vein", PACE, Vol. 16, June 1993, pp. 1349-1353, incorporated herein by reference, a severed lead tip may migrate through the bloodstream, possibly resulting in serious complications. Thus it is imperative that any device for lead extraction remove the entire lead and not just a portion thereof. SUMMARY OF THE INVENTION Thus it is an object of the present invention to remove an implanted object affixed by fibrous scar tissue in a body. It is a further object of the present invention to remove an implanted object affixed by fibrous scar tissue in a body with a laser. It is a still further object of the present invention to use a laser catheter which is guided by the implanted object to a location proximate the fibrous scar tissue. In accordance with the above objects there is provided a lead extraction system which utilizes a laser energy source to separate an implanted object, such as a pacemaker lead, from fibrous scar tissue and thereby permit the implanted object to be extracted from a body. The extraction system features a catheter having a central lumen. The lumen is preferably dimensioned so a pacemaker lead will fit within. The catheter is thereby guided by the lead. The catheter has at least one optical fiber to emit laser energy from the distal end and thereby separate the lead from fibrous scar tissue. Embodiments of the present invention include catheters which emit light parallel as well as inwardly perpendicular to the catheter and the lead. Through such catheters the lead may be separated along its length, as well as separated at its distal end from fibrous scar tissue, thereby permitting the lead to be readily extracted from the body. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is depicts a lead placed in the venous system and having its distal tip located in the heart. FIG. 2 is a plan view of an implanted object extractor system constructed in according to the present invention. FIG. 3 is a sectional view of the catheter of the system shown in FIG. 2 taken along the lines 3-3. FIG. 4 is a sectional view of the catheter of the system shown in FIG. 2 taken along the lines 4-4. FIG. 5 is a sectional view of the catheter of the system shown in FIG. 2 taken along the lines 5-5. FIG. 6 is a sectional view of the catheter of the system shown in FIG. 2 taken along the lines 6-6. FIG. 7 is a side plan detail view of the distal portion of the catheter of FIG. 2 as it would be used to remove a lead. FIG. 8 is a side sectional view of the distal portion of an implanted lead showing the formation of fibrous scar tissue. FIG. 9 is a side sectional view of the distal portion of an implanted lead showing a laser extractor for an implanted object of the present invention removing fibrous scar tissue. FIG. 10 is a side sectional view of the distal portion a laser extractor for an implanted object of the present invention. FIG. 10A is a side sectional view of the distal portion of an alternate embodiment of a laser extractor for an implanted object of the present invention. FIG. 10B is an enlarged side sectional view of the distal portion of an alternate embodiment of a laser extractor for an implanted object of the present invention. FIG. 11 is a side sectional view of the distal portion of an alternate embodiment of a laser extractor for an implanted object of the present invention. FIG. 12 is a side sectional view of the distal portion of an alternate embodiment of a laser extractor for an implanted object of the present invention. FIG. 13 is a side sectional view of the distal portion of an implanted lead showing the formation of fibrous scar tissue separating the electrode tip from direct contact with heart tissue. FIG. 14 is a side sectional view of the distal portion of an implanted lead showing an alternate embodiment of a laser extractor for an implanted object of the present invention removing fibrous scar tissue. FIG. 15 is a plan view of an alternate embodiment of a laser extractor for an implanted object of the present invention. FIG. 16 is a detail of the distal end of an alternative embodiment of a laser extractor for an implanted object of the present invention. FIG. 17 is a detail of the distal end of an alternative embodiment of a laser extractor for an implanted object of the present invention. FIG. 18 is a detail of a cross-sectional view of an alternative embodiment of a laser extractor for an implanted object of the present invention. FIG. 19 is a detail of a cross-sectional view of an alternative embodiment of a laser extractor for an implanted object of the present invention. FIG. 20 is a schematic block diagram of an alternative embodiment of a laser extractor for an implanted object of the present invention which provides synchronized laser control to the cardiac cycle. FIG. 21 is a detailed schematic block diagram of a trigger generator used in the device shown in FIG. 20. FIG. 22 is a detailed schematic block diagram of a laser firing circuit used in the device shown in FIG. 20. FIG. 23 is a detailed schematic block diagram of a laser unit used in the device shown in FIG. 20. FIG. 24 illustrates a ECG signal, marker pulse, trigger pulse and firing pulse waveforms occurring in the device depicted in FIG. 20. FIG. 25 illustrates a touch sensitive monitor which may be used in the device depicted in FIG. 20. FIG. 26 is a detailed schematic diagram of the trigger pulse circuit, pulse positioning circuit, pulse width circuit and laser firing circuit depicted in FIGS. 20-23. FIG. 27 is a plan view of an alternate embodiment of a laser extractor for an implanted object of the present invention incorporating a sensing electrical lead. The drawings are not necessarily to scale. DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning to the FIGS., the present invention comprises generally a catheter 1 configured to remove an implanted object from a patient's body, and especially designed to remove an implanted pacemaker lead from a patient's venous system and heart. As seen in FIG. 1 a typical transvenous endocardial lead 2 connects a pacemaker 3 to heart 10 through right subclavian vein 4, superior vena cava 5 and down into heart 10. Transvenous endocardial lead 2 is shown specifically in right ventricle 12, although leads to right atrium 11 are often used also. Distal end 13 of lead 2 includes an electrode 14 for electrically stimulating heart 10 and a plurality of tines 15 to provide fixation of lead 2 within heart 10. As discussed above, during chronic implantation lead 2 becomes affixed along its side surfaces 20 to inner surfaces 21 of the venous system and at its distal end 13 to heart 10 through the formation of fibrous scar tissue 22. Catheter 1 is designed to separate such fibrous scar tissue 22 from lead 2 and has a series of optical fibers 23 running throughout. Optical fibers 23 are connected at their proximal end 42 to a laser energy source 8 by coupler 44 and are arranged to emit laser energy 64 from distal end 25 of catheter 1. Catheter body 30 has a guide lumen 31 configured to permit catheter 1 to be introduced over lead 2 and be guided thereby. Specifically guide lumen 31 extends from distal end 25 of catheter 1 to proximal end 17 of catheter body 30. Catheter 1 further features stylet tube 50 to permit catheter 1 to be further guided, steered or pushed by a stylet (not shown.) Distal end 25 of catheter 1 preferably features an annular series of optical fibers 23 which thereby provide an annular source of laser energy about the circumference of lead 2 which defines a tissue-removal region 123 (depicted in FIG. 10B described below) the tissue- removal region 123 only extending between the interior surface of catheter 1 and the exterior surface of said catheter 1. Through such an arrangement catheter 1 may be guided along lead 2 permitting laser energy 64 emitted from optical fibers 23 to ablate any fibrous scar tissue 22 affixing lead 2 within the venous system and heart 10 without laser energy 64 also damaging lead 2 or the vessel walls. FIG. 2 depicts catheter 1. As seen, catheter 1 comprises catheter body 30, bifurcate cover 40 and stylet leg 41 extending therefrom, and at least one optical fiber 23. The optical fiber or fibers 23 used are preferably a 130 micron fiber available from the Spectranetics Corporation in Colorado Springs, Colorado, USA. The specific optical fibers used, however, are not within the scope of the claimed invention and any optical fiber suitable to transmit laser energy to ablate fibrous scar tissue may be used. Located at proximal end 42 of optical fibers 23 sits coupler 44. Coupler 44 permits optical fibers 23 to be coupled to a laser energy source 8. Laser energy source 8 is preferably a xenon-chloride excimer laser such as model no. CVX-300 available from the Spectranetics Corporation, discussed above. In the preferred embodiment laser energy source 8 emits laser energy in the wavelength of between 193 to 351 nanometers with 308 nanometers preferred having an energy of 60 millijoules per square millimeter at a rate of 30 pulses per second delivered in groups of 5 seconds duration with 15 seconds pause between each group. Coupler 44 may be of any configuration known in the art. A suitable coupler 44 may also be obtained from Spectranetics Corporation. Bifurcate cover 40 cooperates with skirt 45 to feed optical fibers 23 into catheter body 30 as well as stylet leg 41 into stylet tube 50 in catheter body 30. Proximal end 48 of stylet leg 41 has stylet introducer 51. Catheter body 30, as seen shown in cross section in FIGS. 3-6, has guide lumen 31 running throughout and is preferably constructed from a biocompatible material, such as polyurethane. Positioned within catheter body 30 are optical fibers 23 and stylet tube 50. Stylet tube 50 permits a stylet to be introduced through catheter body 30 and thereby move catheter 1 through the venous system. In a preferred embodiment a steerable stylet may be used with the disclosed invention, such as the steerable stylet disclosed in U.S. Patent Application Serial No. 08/069,310 of Brennan et al. entitled "Steerable Stylet and Manipulative Handle Assembly" and filed May 28, 1993, incorporated herein by reference. Additionally a lead extender (not shown) may be provided to permit traction to be applied along lead throughout guide lumen 31. Specifically the lead extender would be attached to lead 2 and passed from distal end 25 of catheter 1 through guide lumen 31 and exiting at proximal end 17 of catheter body 30. Extender may be any suitable object, such as a suture or wedging stylet, which may be attached to lead and passed through guide lumen 31 to permit the application of traction to proximal distal end of lead. As seen in FIGS. 5 and 6 optical fibers 23 are positioned within catheter body 30 so as to have an annular arrangement at distal end 25 of catheter 1. In such a fashion optical fibers 23 are arranged so as to emit laser energy 64 in a tissue-removal region (designated 123 in FIG. 10B) and thus onto fibrous scar tissue 22 encapsulating lead 2, specifically along body 6 of lead 2, or affixed to distal end 13 of lead 2 as seen in FIGS. 7 and 9, and ablate it. In such a fashion lead 2 may be freed and removed from a patient's body without laser energy 64 also ablating lead insulation or a vessel wall. In a preferred embodiment optical fibers 23 are arranged in a spiral fashion about the length of catheter body 30 to provide flexibility. In a further embodiment optical fibers 23 may also be arranged in an annular fashion throughout the length of catheter body 30. In such a manner the overall diameter of catheter body 30 may be decreased, as well as the overall ability of catheter body 30 to be pushed along lead 2. Moreover, optical fibers 23 may also be incorporated as one fiber bundle throughout catheter body 30 and separated in an annular arrangement around distal end 25. Detail of distal end 25 of catheter 1 is shown in FIG. 10. As seen distal end 25 of catheter 1 features a guard assembly 68. Guard assembly 68 is constructed from outer jacket 61 and inner sleeve 62. Specifically the distal end 43 of each optical fiber 23 is sandwiched between guard band 53 and guard ring 54. Guard band 53 is preferably made from a platinum iridium alloy and preferably has an outer taper 55 of 30 to 60 degrees. Guard ring 54 is preferably made from stainless steel and preferably has an inner taper 60 of 30 to 60 degrees. Distal end 43 of optical fibers 23 are recessed, preferably 1 millimeter, from distal end 46 of guard band 53 and distal end 47 of guard ring 54, as best seen in FIG. 10, although distal end of optical fibers 43 may also be flush with distal end 46 of guard band 53 and distal end 47 of guard ring 54, as best seen in FIG. 10A. Guard band 53 is preferably seven one-thousandths of an inch (7/1000") while guard ring 54 is preferably three one-thousandths of an inch (3/1000"). As discussed above, optical fiber 23 is preferably a 130 micron fiber (five one-thousandths of an inch-5/1000") . Thus, in the preferred embodiment, guard ring 54 has a radial (i.e. measured along a radial line from the center of lumen 31) thickness less than the radial thickness of optical fiber 23. Although guard ring 54 radial thickness is shown as less than the radial thickness of optical fiber 23, it is also possible to have guard ring 54 to have the same thickness as optical fiber 23. The geometry and relative dimensions of optical fiber 23 and guard assembly 68 are important in order to minimize the photo degradation of lead 2 from laser energy 64. This is important because if lead 2 insulation is ablated away, the coiled conductor could become exposed and possibly unwind. As detailed above such a situation is undesirable. This feature further minimizes the possible emission of by-products from the photo degradation of lead, and in particular by-products from the photo degradation of lead insulation, into the blood stream. In addition, cutting into lead insulation may cause a slice of the insulative material to fold back and become wedged between the lead and the inner lumen of the catheter. In such a manner the catheter may become stuck in place along the lead. Guard band 53 and guard ring 54, because they are constructed from radiopaque materials, also provide a convenient marker of the position of distal end 25 of catheter 1 when using a fluoroscope. Outer jacket 61 and inner sleeve 62 are preferably made from a biocompatible material, such as polyurethane. Outer jacket 61 and inner sleeve 62 may further be formed integral with catheter body 30. FIG. 10B is an enlarged side sectional view of the distal portion of an alternate embodiment of a laser extractor for an implanted object of the present invention. Such an alternate embodiment is used in a system as shown in FIG. 1. As seen distal end 25 of catheter 1 features a guard assembly 68. Guard assembly 68 is constructed from outer jacket 61 and inner sleeve 62. Specifically distal end 43 of each optical fiber 23 is sandwiched between guard band 53 and guard ring 54. As discussed above, guard band 53 is preferably made from a platinum iridium alloy and preferably has an outer taper 55 of 30 to 60 degrees. Guard ring 54 is preferably made from stainless steel and has an inner taper 60 of 30 of 60 degrees. Distal end 43 of optical fibers 23 may or may not be recessed from the distal end of the guard assembly. In particular the exact relation of distal end 43 of optical fibers 23, as well as the relative thicknesses of each of guard band 53, guard ring 54 and optical fiber 23 arid the wavelength and power of the laser energy used are coordinated so the laser energy defines a tissue-removal region 123. As seen, through the proper selection of relation of distal end 43 of optical fibers 23, as well as the relative thicknesses of each of the guard band 53, guard ring 54 and optical fiber 23 and the wavelength and power of laser 8, tissue-removal region 123 extends completely within region bounded by outer surface 161 and inner surface 131 of catheter 1 when the catheter is within the fluids of the venous system. Thus through such a configuration the extractor system of the present invention only removes tissue surrounding lead 2 (shown here in phantom) and will not cut into lead 2. As discussed above, the geometry and relative dimensions and specifications of optical fiber 23, guard assembly 68 and laser 8 are important in order to minimize the photo degradation of lead 2 from laser energy 64. As discussed above, this is important because if lead 2 insulation is ablated away, the coiled conductor could become exposed and possibly unwind; possibly harmful by-products from the photo degradation of lead may be emitted into the blood stream as well as possibly cutting into lead insulation and causing a slice of the insulative material to fold back and become wedged between the lead and the inner lumen of the catheter. In addition tissue-removal region 123 permits catheter 1 to be moved along the length of lead 2 without becoming stuck or blocked by the presence of fibrotic tissue within catheter lumen. Guard band 53 and guard ring 54 are constructed from radiopaque materials. Outer jacket 61 and inner sleeve 62 are preferably made from a biocompatible material, such as polyurethane. Outer jacket 61 and inner sleeve 62 may further be formed integral with catheter body 30. A further embodiment of a distal end 25 of catheter 1 is shown in FIG. 11. This embodiment is substantially the same as that shown in FIG. 10 but for the reverse outer taper 55 at distal end 46 of guard band 53 and reverse inner taper 60 at distal end 47 of guard ring 54. Through such a configuration it is believed that as catheter 1 contacts fibrous scar tissue or channel scar along body 6 of lead 2, reverse tapers 55, 60 function to direct or plow such tissue toward distal end 43 of optical fibers 23 and thereby be ablated by laser energy 64. A further embodiment of a distal end 25 of catheter 1 is shown in FIG. 12. This embodiment is substantially the same as that shown in FIG. 10 but for bevelled surface 63 along distal end 43 of optical fibers 23. Through bevelled surface 63 laser energy 64 is emitted from optical fibers 23 in a direction other than parallel to distal end 25 of catheter 1. As seen bevelled surface 63 depicted in FIG. 11 causes laser energy, shown by arrows 64 to be emitted towards the center of guide lumen 31 of catheter 1. Such an emission of light is especially useful to free distal end 13 of lead 2 affixed by fibrous scar tissue 22 as seen in FIGS. 13 and 14. As seen in FIG. 13, lead 2 is affixed by fibrous scar tissue 22 away from heart tissue 26. Through a catheter 1 having bevelled surface 63 along distal end 43 of optical fibers 23, as seen in FIG. 14, fibrous scar tissue 22 proximate distal end 13 of lead 2 and especially along the face of electrode 14 may be ablated thereby completely freeing lead 2. A further embodiment of catheter 1 is shown in FIG. 15. As seen this embodiment is substantially similar to that shown in FIG. 2 with the exception it does not feature stylet introducer 51, stylet leg 41 or stylet tube 50. Still further embodiments of catheter 1 are shown in FIGS. 16 and 17. The embodiment depicted in FIG. 16 is substantially similar to those previously described with the exception of utilizing only a single optical fiber 23 and distal end 25 having an asymmetrical cross section. The embodiment depicted in FIG. 17 is similar to that shown in FIG. 16 with the exception that optical fiber 23 is curved at its distal end, as best viewed in FIG. 19. These embodiments, because only a single optical fiber is used, allow precise and controlled ablation of fibrous scar tissue 22 affixing lead 2, especially in conjunction with a stylet located in stylet tube 50 used to rotate catheter 1 about lead 2. Furthermore means may be provided to manipulate optical fiber 23, such as that disclosed in the U.S. Patent No. 5,203,779 and U.S. Patent No. 5,041,108, each incorporated herein by reference. Each of the embodiments discussed above may further feature a series of centering tabs 58 within the lumen of catheter 1, preferably near the distal end. These centering tabs 58 may be best seen in FIG. 18. Tabs 58 assist in avoiding the inadvertent vaporization of lead 6 by the emitted laser energy 64. Other devices, such as a series of leaf springs longitudinally aligned with catheter 1 may also be used. Operation of catheter 1 to extract an implanted object, and specifically a lead 2, is as follows. The proximal end of lead 2 is uncovered surgically so that catheter 1 may be introduced over it. Next proximal end of lead 2 is introduced into guide lumen 31. If needed, this may be accomplished by removing connector pin assembly 38 from proximal end of lead 2, affixing an extender which extends throughout guide lumen 31 to lead 2, as discussed above, and through traction along extender, introducing lead 2 within guide lumen 31. Additionally, besides affixing an extender, a locking stylet may also be introduced into the center lumen of lead 2 so as to provide traction to the distal end of the lead. This effectively supports the lead and prevents excessive longitudinal force along the lead body, and thus the insulation, from causing the lead to uncoil. Once catheter 1 is positioned so lead 2 extends through guide lumen 31, catheter 1 is moved until distal end 25 of catheter 1 is proximate fibrous scar tissue 22. As represented in FIG. 7, laser energy 64 from a laser (not shown) is transmitted through optical fibers 23 and onto fibrous scar tissue 22 located within tissue-removal region 123 (depicted in FIG. 10B) thereby ablating fibrous scar tissue 22 and releasing lead 2 in the area proximate distal end 25 of catheter 1. Catheter 1 is repositioned until once again distal end 25 of catheter 1 is proximate fibrous scar tissue 22. Transmission of laser energy 64 onto fibrous scar tissue 22 is repeated along the entire length of lead 2 until lead 2 is no longer affixed by fibrous scar tissue 22 along its side surface 20. As seen in FIG. 9 laser energy 64, besides ablating fibrous scar tissue 22, also ablates and cuts through tines 15, particularly if tines 15 are constructed from common lead materials, such as silicone or polyurethane. Once side surface 20 of lead 2 is released from fibrous scar tissue 22, only fibrous scar tissue proximate distal end 13 of lead 2 at distal face of electrode 14 retains lead, as shown in FIG. 9. At this point traction may be applied to either proximal end of lead 2 or to a point proximal distal end of lead 2, such as through a counter traction stylet as disclosed in U.S. Patent Nos. 5,207,683; 5,013,310; 4,988,347 and 4,943,289 to Goode et al. to withdraw lead 2 from fibrous scar tissue 22 and thereby accomplish lead 2 removal. Use may also be made of a sheath, such as that disclosed in U.S. Patent No. 5,011,482 to Goode et al., to overlay lead 2 during traction and apply counter traction at a site near the electrode to confine the traction force to an area within the sheath. In addition, catheter 1 as shown in FIG. 12 having inwardly projecting laser energy 64 may also be used to completely free distal end 13 of lead 2. Specifically this embodiment is positioned along lead 2 as shown in FIG. 14 such that laser energy 64 emitted by bevelled surfaces 63 of optical fibers 23 separates lead 2 as shown. In an alternate embodiment of the present invention, shown in FIGS. 20-27, the laser used with the catheter is controlled in synchrony with heart 10. As discussed above synchronization of the laser with the cardiac cycle offers several advantages. First, a laser pulse striking the heart tissue may, if it occurs at a delicate time in the cardiac cycle, such as during the T wave of the ECG, could cause the heart to fibrillate and result in heart failure. Synchronization permits the emission of laser energy proximate the cardiac tissue to be controlled so as to avoid striking the heart at any delicate time in the cardiac cycle. And specifically to avoid having the laser energized at a time during which the cardiac tissue may contract towards the laser and thus cause the laser energy to unintentionally strike the cardiac tissue. Such control would be most desirable during the time of removal when the distal end of the catheter is proximate the heart tissue. Secondly the constant motion of the heart may cause difficulties in reliably positioning a laser beam. Synchronization permits the emission of laser energy to be emitted only during times of the cardiac cycle during which movement caused by contractions will not result in problems. Thirdly laser ablation has been found to be most effective when the tissue to be ablated is positioned immediate the tip of the optical fibers. Thus a longitudinal force between the catheter tip and the fibrotic tissue will promote rapid and efficient tissue ablation. Synchronization will thus also permit the emission of laser energy to be timed with the cardiac contractions so as to occur at the most desirable times. Such synchronization would be most desirable during the time of removal when the distal end of the catheter is not proximate the heart tissue but during which cardiac contractions would tend to force the fibrotic tissue towards catheter 1. FIGS. 20-27 depict a device which provides control of the laser in synchrony with heart 10. An overview of such a device is shown in FIG. 20 and is seen to comprise essentially a component to sense cardiac cycle 212, a component to generate a trigger pulse for the laser in response to sensed cardiac cycle 218, a component to position the leading edge of the trigger pulse at a specified time within cardiac cycle 232, a component to define the width of the trigger pulse to occur during cardiac cycle 234, and a component to control the firing of the laser in response to the trigger pulse and for a period response to the defined width 222. In particular, electrocardiogram (ECG) unit 212 electrically connects to heart 10 of a patient so as to sense the cardiac cycle and provide ECG signal 216. ECG unit 212 may be connected to the heart in any known manner for sensing cardiac signals including surface mounted electrodes as well as internal or intracavitary electrodes. In addition the sensing connection may further be incorporated integrally with the catheter 1, such as through the provision of an electrical lead with catheter 1, and especially at the tip of the catheter 1. Specifically as seen in FIG. 27 catheter 1 has a sensing lead 390 integral therewith. Lead 390 has electrode 391 at distal end. Electrode may be either of unipolar design, in which case a surface contact may be used or bipolar design. As seen lead 390 extends through catheter 1 and exits past cover 40. Lead 390 may then be connected to the ECG unit 212 and communicate sensed signals 216 thereto. Signal 216 is delivered to trigger generator 218. Trigger generator 218 provides a trigger pulse 220 to laser firing circuit 222. Laser firing circuit 222 energizes laser unit 224. The position of trigger pulse 220 in the heartbeat cycle of ECG signal 216 is determined by pulse positioning circuit 232. The width of pulse 220 and its duration during the heartbeat cycle is determined by pulse width circuit 234. Trigger generator 218, as well as pulse positioning circuit 232 and pulse width circuit 234, may be included as an additional board in a PC or a microprocessor 236, in which case the system can be controlled through the computer keyboard and suitable software. PC 236 and ECG 212 may have separate monitors, or they may have a single monitor 238 which displays both the ECG and information about the trigger pulse 220. Trigger generator 218 may include a marker pulse circuit 250 which provides marker pulse 252 and trigger pulse circuit 254 which responds to marker pulse 252 to create trigger pulse 220. Alternatively, marker pulse circuit 250 is included in the ECG itself in some cases. This can be better understood with reference to FIG. 24, where ECG signal 216 may be seen as consisting of a series of heartbeat cycles 256a, 256b, 256c each of which contains the waveforms Q, R, S and T. Where waveform R crosses preselected threshold 258, marker pulses 252a, 252b, 252c are created. Trigger pulses 220a, 220b, 220c are then created by trigger pulse circuit 254. The position of the leading edge 260 and the overall width 262 of each trigger pulse 220 is determined respectively by pulse positioning circuit 232 and pulse width circuit 234. In response to trigger pulse 220, a firing pulse 264 indicated as 264a, 264b and 264c, FIG. 24, is created to energize laser 224. In FIG. 22, laser firing circuit 222 is shown to include gate 270 which generally inhibits the delivery of trigger circuit 220 to laser power supply 272 in laser unit 224. The inhibiting effect of gate 270 can be overcome when the operator activates a switch 274. Trigger pulse 220 is still inhibited, however, by arming circuit 276 which in turn can have its inhibiting effect overcome by the operation of arming switch 278. This double lock on the delivery of trigger pulse 220 to laser power supply 272 ensures that the firing of the laser is truly desired and not accidental. Thus the operator must first arm the system by operating arming switch 278 to enable arming circuit 276. Then and only then is he able to pass the next occurring trigger pulse 220 through gate 270 to the laser power supply 272 by actuating switch 274. Laser unit 224, although not shown in detail should be understood to comprise a laser power supply and a laser, as best seen in FIG. 23, to produce a pulsed laser beam through catheter 1 and thereby remove an implanted object. The output of laser 280 is delivered through optical fiber 23 to catheter 1. Monitor 238, FIG. 25, may display both the ECG signal 216 and the display of the delay 284 switch has been introduced by pulse positioning circuit 232, FIG. 20, which delay is indicated as one millisecond in FIG. 25. Monitor 238 may also include pulse width 286 shown as 50 milliseconds selected by pulse width circuit 234, FIG. 20. Monitor 238 may further include a delay selection switch 288 which when pressed enables one to increase or decrease the delay time by simply touching the up 290 or down 292 arrows on the screen. Pulse width touch which 294 may be used in the same fashion to adjust the pulse width duration. A detailed schematic of a trigger pulse circuit 254 suitable for use in the present invention is depicted in FIG. 26. Trigger pulse width circuit 254 may include an anti- false trigger pulse circuit 300 to prevent a false firing or second firing of the system when a firing sequence is already in progress. Also included in trigger pulse circuit 254 is a delay timer 302 and a pulse width timer 304. When marker pulse 252 on line 306 is permitted to pass through anti-false trigger pulse circuit 300, marker pulse 252 is input on line 308 to delay timer 302. The conjunction of marker pulse 252 with the input on line 310 from 10 KHz clock 312 causes delay timer 302 to set the position of the leading edge of the trigger pulse 220. The appearance of marker pulse 252 on line 308 also is delivered as an enable signal on line 314 to preset pulse width timer 304. When the leading edge position of trigger pulse 220 has been set by delay timer 302 a signal is provided on line 316 to AND gate 318, which in conjunction with a signal from clock 312 causes trigger pulse 220 to be expanded to a predetermined width in pulse width timer 304. The specific positioning of the leading edge of the trigger pulse by delay timer 302 is controlled by pulse positioning circuit 232 which is typically a time delay data latch under control of the computer via the data bus 320. Similarly, the duration of the pulse imparted by pulse width timer 304 is controlled by pulse width circuit 234, typically a pulse width time data width circuit 234, typically a pulse width time data latch under control of the microprocessor or PC via bus 322. The trigger pulse 220 then is delivered over line 324 to gate 270 which may include simply an AND gate 326. Arming circuit 276 includes flip-flop 328, invertor 330, and OR gate 332. When arming switch 278 is actuated, the signal to invertor 330 resets flip-flop 328 so that now there is a proper output on line 334 from flip-flop 328 into OR gate 332 as well as the proper input from arming switch 278 on line 336 into OR gate 332. Thus, when next the trigger pulse arrives on line 324, if the operator operates switch 274 the pulse will be passed through AND gate 326 and OR gate 332 to pass the trigger pulse on line 340 to laser power supply 272. When the trigger pulse passing through OR gate 332 ends, the clock input to flip-flop 328 is no longer enabled and the output on line 334 ceases so that OR gate 332 is no longer enabled to pass subsequent trigger pulses to line 340 and laser power supply 273. The anti-false trigger pulse circuit 300 uses a flip- flop 350, two invertors 352 and 354, and two OR gates 356 and 358. When a trigger pulse is supplied on line 324 by pulse width timer 304, it is also simultaneously placed on line 360 which is connected to invertor 354 and to OR gate 356. At the end of the trigger pulse, the proper level appears on line 360 to enable OR gate 356 and to reset flip-flop 350 through invertor 354 and OR gate 358. When flip-flop 350 is reset it provides a second enabling input on line 362 to OR gate 356. Thus, when next a marker pulse 252 is delivered on line 306 and passed by invertor 352 to OR gate 356, it is passed to line 308 and thus on to delay timer 302. The marker pulse 252 appearing on line 308 also clocks flip-flop 350 so that the proper signal is no longer on line 362 and AND gate 356 is disabled. Until a reset occurs from the software on line 366 or the end of the trigger pulse level occurs on line 360 no further marker pulses will be passed. While the embodiments of the present invention have been described in particular application to a laser extractor for a cardiac lead, it will also be understood the invention may be practiced to remove other implanted objects, including but not limited to such other implanted objects as stents. Moreover, although the invention has been described in detail with particular reference to a preferred embodiment and alternate embodiments thereof, it will be understood variations and modifications can be effected within the scope of the following claims. Such modifications may include substituting elements or components which perform substantially the same function in substantially the same way to achieve substantially the same result for those described herein.

Claims: WHAT IS CLAIMED IS: 1. A system for removing an object from the venous system comprising: a catheter having a distal end and a proximal end, the catheter having a tubular portion having a center lumen, the catheter distal end having a guard band positioned about an exterior surface of the elongated catheter, the catheter distal end having a guard ring positioned about an interior surface of the catheter; at least one optical fiber supported by the tubular portion the optical fiber distal end extending between the guard band and the guard ring; and a source of laser energy communicating with the optical fiber and transmitting laser energy through the optical fiber and beyond the optical fiber distal end into a tissue-removal region, the tissue-removal region only extending between the interior surface of the catheter and the exterior surface of the catheter. 2. The system of claim l further comprising a stylet port in the catheter to permit a stylet to be mated with the catheter. 3. The system of claim 1 further comprising the optical fiber extending to the region proximate the catheter distal end in a first direction relative to the catheter. 4. The system of claim 3 wherein the first direction being towards the lumen of the catheter. 5. The system of claim 1 further comprising the distal end of the catheter being radiopaque. 6. The system of claim 1 wherein the optical fiber distal end is spaced proximally from the guard ring distal end. 7. The system of claim 1 wherein the catheter further comprises means for sensing cardiac signals. 8. The system of claim 7 wherein the means for sensing cardiac signals comprises means for providing an electrical connection with the heart. 9. The system of claim 1 further comprising means for sensing cardiac signals and means for synchronizing the transmission of the laser energy to the sensed cardiac signals. 10. The system of claim 9 wherein the means for synchronizing the transmission of the laser energy to the sensed cardiac signals further comprises a means to generate a trigger pulse for the laser in response to the sensed cardiac signals. 11. The system of claim 9 wherein the means for synchronizing the transmission of the laser energy to the sensed cardiac signals further comprises a means to position the leading edge of the trigger pulse at a specified time, a means to define the width of the trigger pulse, and a means to control the firing of the laser in response to the trigger pulse and for the defined width. 12. The system of claim 1 wherein the guard ring distal end and guard band distal end are positioned at the catheter distal end. 13. The system of claim 1 wherein the guard ring the distal end has a taper. 14. The system of claim 1 wherein the guard band distal end has a taper. 15. The system of claim 1 wherein the optical fiber has a radial thickness and the guard ring has a radial thickness equal to or less than the radial thickness of the optical fiber. 16. The system of claim 1 wherein the laser energy is transmitted beyond the optical fiber distal end into the tissue-removal region within fluids of the venous system. 17. A system for removing an object from the venous system comprising: a catheter having a distal end and a proximal end, the catheter having a tubular portion having a center lumen, the catheter distal end having a guard band positioned about an exterior surface of the elongated catheter, the guard band having a distal end, the catheter distal end having a guard ring positioned about an interior surface of the elongated catheter, the guard ring having a distal end; at least one optical fiber supported by the tubular portion, the optical fiber has a distal end, the optical fiber distal end extending between the guard band and the guard ring, the optical fiber distal end spaced proximally from the guard band distal end; and a source of laser energy communicating with the optical fiber so that the light energy will be transmitted to the region proximate the distal end of the catheter. 18. The system of claim 17 wherein the source of laser energy transmits laser energy beyond the optical fiber distal end into a tissue-removal region, the tissue-removal region only extending between the interior surface of the catheter and the exterior surface of the catheter. 19. The system of claim 17 further comprising the optical fiber extending to the region proximate the distal end in a direction towards the lumen of the catheter. 20. The system of claim 17 wherein the optical fiber distal end is spaced proximally from the guard ring distal end. 21. The system of claim 17 wherein the catheter further comprises means for sensing cardiac signals. 22. The system of claim 21 wherein the means for sensing cardiac signals comprises means for providing an electrical connection with the heart. 23. The system of claim 17 further comprising means for sensing cardiac signals and means for synchronizing the transmission of the laser energy to the sensed cardiac signals. 24. The system of claim 23 wherein the means for synchronizing the transmission of the laser energy to the sensed cardiac signals further comprises a means to generate a trigger pulse for the laser in response to the sensed cardiac signals. 25. The system of claim 24 wherein the means for synchronizing the transmission of the laser energy to the sensed cardiac signals further comprises a means to position the leading edge of the trigger pulse at a specified time, a means to define the width of the trigger pulse, and a means to control the firing of the laser in response to the trigger pulse and for the defined width. 26. The system of claim 17 wherein the optical fiber has a radial thickness and the guard ring has a radial thickness equal to or less than the radial thickness of the optical fiber. 27. A method for removing an implanted object affixed to a body by fibrous scar tissue comprising the steps of: introducing a catheter having a lumen and at least one optical fiber into the venous system, the catheter further having a distal end having a guard assembly, the guard assembly comprising a guard band positioned about an exterior surface of the catheter and a guard ring positioned about an interior surface of the catheter, the optical fiber extending between the guard band and the guard ring; positioning the implanted object within the lumen of the catheter; positioning the distal end of the catheter proximate the fibrous scar tissue; transmitting laser energy through the optical fiber beyond the optical fiber distal end into a tissue-removal region, the tissue-removal region only extending between the interior surface of the catheter and the exterior surface of the catheter; moving the catheter along the implanted object as the fibrous scar tissue releases the implanted object; and removing the object from the venous system. 28. The method of claim 27 further comprising the step of providing a stylet lumen in the catheter body. 29. The method of claim 27 further comprising the step of steering the catheter body along the implanted object. 30. The method of claim 27 further comprising the step of providing an optical fiber which emits laser energy away from the implanted object. 31. The method of claim 27 further comprising the step of providing the distal end of the optical fiber at a position proximal to the distal end of the guard ring. 32. The method of claim 27 wherein the implanted object is a pacemaker lead. 33. The method of claim 27 further comprising the steps of sensing cardiac signals and synchronizing to the sensed cardiac signals the energizing of a laser connected to the optical fiber to cause laser energy to be emitted into the fibrous scar tissue. 34. A device for removing an object from the venous system comprising: a catheter having a lumen, a distal end and a proximal end, the catheter, the distal end having a guard assembly, the guard assembly comprising a guard band positioned about an exterior surface of the catheter and a guard ring positioned about an interior surface of the catheter; at least one optical fiber supported by the catheter, the optical fiber extending to a region proximate the distal end of the catheter, the optical fiber extending between the guard band and the guard ring, the optical fiber having a radial thickness, the guard ring having a radial thickness equal to or less than the radial thickness of the optical fiber; and a source of laser energy communicating with the optical fiber so that the light energy will be transmitted to the region proximate the distal end of the catheter. 35. The system of claim 34 wherein the catheter further comprises means for sensing cardiac signals. 36. The system of claim 35 wherein the means for sensing cardiac signals comprises means for providing an electrical connection with the heart. 37. The system of claim 36 further comprising means for sensing cardiac signals and means for synchronizing the transmission of the laser energy to the sensed cardiac signals. 38. The system of claim 37 wherein the means for synchronizing the transmission of the laser energy to the sensed cardiac signals further comprises a means to generate a trigger pulse for the laser in response to the sensed cardiac signals. 39. The system of claim 34 wherein the guard ring distal end and guard band distal end are positioned at the catheter distal end. 40. The system of claim 34 wherein the guard ring has a distal end, the distal end has a taper. 41. The system of claim 34 wherein the optical fiber distal end is spaced proximally from the guard ring distal end.

Inventors: WAHLSTROM DALE A, WILLIAMS TERRELL M, WAHLSTROM, DALE, A., WILLIAMS, TERRELL, M.
Applicants: MEDTRONIC INC, WAHLSTROM DALE A, WILLIAMS TERRELL M, MEDTRONIC, INC., WAHLSTROM, DALE, A., WILLIAMS, TERRELL, M.
Application year: 1994
Main classification: A61B17
IPC codes: A61B17, A61B18, A61B19, A61N1